111 research outputs found
ALMA reveals the feeding of the Seyfert 1 nucleus in NGC 1566
We report ALMA observations of CO(3-2) emission in the Seyfert 1 galaxy NGC
1566, at a spatial resolution of 25 pc. Our aim is to investigate the
morphology and dynamics of the gas inside the central kpc, and to probe nuclear
fueling and feedback phenomena. NGC 1566 has a nuclear bar of 1.7 kpc radius
and a conspicuous grand design spiral starting from this radius. The ALMA field
of view, of diameter 0.9 kpc, lies well inside the nuclear bar and reveals a
molecular trailing spiral structure from 50 to 300~pc in size, which is
contributing to fuel the nucleus, according to its negative gravity torques.
The spiral starts with a large pitch angle from the center and then winds up
in a pseudo-ring at the inner Lindblad resonance (ILR) of the nuclear bar.
This is the first time that a trailing spiral structure is clearly seen
driving the gas inwards inside the ILR ring of the nuclear bar. This phenomenon
shows that the massive central black hole has a significant dynamical influence
on the gas, triggering its fueling.
The gaseous spiral is well correlated with the dusty spiral seen through
extinction in HST images, and also with a spiral feature emitting 0.87mm
continuum. This continuum emission must come essentially from cold dust heated
by the interstellar radiation field. The HCN(4-3) and HCO+(4-3) lines were
simultaneously mapped and detected in the nuclear spiral. The HCO+(4-3) line is
3 times stronger than the HCN(4-3), as expected when star formation excitation
dominates over active galactic nucleus (AGN) heating. The CO(3-2)/HCO+(4-3)
integrated intensity ratio is \sim 100.
The molecular gas is in remarkably regular rotation, with only slight
non-circular motions at the periphery of the nuclear spiral arms. These
perturbations are quite small, and no outflow nor AGN feedback is detected.Comment: 11 pages, 16 figures, accepted in Astronomy and Astrophysic
ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433
We report ALMA observations of CO(3-2) emission in the Seyfert 2
double-barred galaxy NGC1433, at the unprecedented spatial resolution of
0.5"=24 pc. Our aim is to probe AGN feeding and feedback phenomena through the
morphology and dynamics of the gas inside the central kpc. The CO map, which
covers the whole nuclear region (nuclear bar and ring), reveals a nuclear
gaseous spiral structure, inside the nuclear ring encircling the nuclear
stellar bar.
This gaseous spiral is well correlated with the dusty spiral seen in Hubble
Space Telescope images. The nuclear spiral winds up in a pseudo-ring at 200 pc
radius, which might correspond to the inner ILR. Continuum emission is detected
at 0.87 mm only at the very centre, and its origin is more likely thermal dust
emission than non-thermal emission from the AGN. It might correspond to the
molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and
HCO+(4-3) lines were observed simultaneously, but only upper limits are
derived, with a ratio to the CO(3-2) line lower than 1/60 at 3sigma, indicating
a relatively low abundance of very dense gas. The kinematics of the gas over
the nuclear disk reveal rather regular rotation only slightly perturbed by
streaming motions due to the spiral; the primary and secondary bars are too
closely aligned with the galaxy major or minor axis to leave a signature in the
projected velocities. Near the nucleus, there is an intense high-velocity CO
emission feature redshifted to 200 km/s (if located in the plane), with a
blue-shifted counterpart, at 2" (100 pc) from the centre. While the CO spectra
are quite narrow in the centre, this wide component is interpreted as an
outflow involving a molecular mass of 3.6 10^6 Mo and a flow rate 7 Mo/yr. The
flow could be in part driven by the central star formation, but is mainly
boosted by the AGN through its wind or radio jets.Comment: 11 pages, 9 figures, Accepted in Astronomy and Astrophysic
Molecular line emission in NGC1068 imaged with ALMA: II. The chemistry of the dense molecular gas
We present a detailed analysis of ALMA Bands 7 and 9 data of CO, HCO+, HCN
and CS, augmented with Plateau de Bure Interferometer (PdBI) data of the ~ 200
pc circumnuclear disk (CND) and the ~ 1.3 kpc starburst ring (SB ring) of
NGC~1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy. We aim at determining
the physical characteristics of the dense gas present in the CND and whether
the different line intensity ratios we find within the CND as well as between
the CND and the SB ring are due to excitation effects (gas density and
temperature differences) or to a different chemistry. We estimate the column
densities of each species in Local Thermodynamic Equilibrium (LTE). We then
compute large one-dimensional non-LTE radiative transfer grids (using RADEX) by
using first only the CO transitions, and then all the available molecules in
order to constrain the densities, temperatures and column densities within the
CND. We finally present a preliminary set of chemical models to determine the
origin of the gas. We find that in general the gas in the CND is very dense (>
10^5 cm^-3) and hot (T> 150K), with differences especially in the temperature
across the CND. The AGN position has the lowest CO/HCO+, CO/HCN and CO/CS
column density ratios. RADEX analyses seem to indicate that there is chemical
differentiation across the CND. We also find differences between the chemistry
of the SB ring and some regions of the CND; the SB ring is also much colder and
less dense than the CND. Chemical modelling does not succeed in reproducing all
the molecular ratios with one model per region, suggesting the presence of
multi-gas phase components. The LTE, RADEX and chemical analyses all indicate
that more than one gas-phase component is necessary to uniquely fit all the
available molecular ratios within the CND.Comment: Accepted by A&A; please contact the author for a better version of
the pdf where the resolution and positions of figures are as they will appear
in the Journa
Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
We investigate the fueling and the feedback of star formation and nuclear
activity in NGC1068, a nearby (D=14Mpc) Seyfert 2 barred galaxy, by analyzing
the distribution and kinematics of the molecular gas in the disk. We have used
ALMA to map the emission of a set of dense molecular gas tracers (CO(3-2),
CO(6-5), HCN(4-3), HCO+(4-3) and CS(7-6)) and their underlying continuum
emission in the central r ~ 2kpc of NGC1068 with spatial resolutions ~
0.3"-0.5" (~ 20-35pc). Molecular line and dust continuum emissions are detected
from a r ~ 200pc off-centered circumnuclear disk (CND), from the
2.6kpc-diameter bar region, and from the r ~ 1.3kpc starburst (SB) ring. Most
of the emission in HCO+, HCN and CS stems from the CND. Molecular line ratios
show dramatic order-of-magnitude changes inside the CND that are correlated
with the UV/X-ray illumination by the AGN, betraying ongoing feedback. The gas
kinematics from r ~ 50pc out to r ~ 400pc reveal a massive (M_mol ~ 2.7 (+0.9,
-1.2) x 10^7 Msun) outflow in all molecular tracers. The tight correlation
between the ionized gas outflow, the radio jet and the occurrence of outward
motions in the disk suggests that the outflow is AGN-driven. The outflow rate
estimated in the CND, dM/dt ~ 63 (+21, -37) Msun yr^-1, is an order of
magnitude higher than the star formation rate at these radii, confirming that
the outflow is AGN-driven. The power of the AGN is able to account for the
estimated momentum and kinetic luminosity of the outflow. The CND mass load
rate of the CND outflow implies a very short gas depletion time scale of <=1
Myr.Comment: Version accepted for publication in A&A (June 4th). Accepted version.
References (3) added and minor typos corrected. 24 pages, 20 figure
ALMA resolves the torus of NGC 1068: continuum and molecular line emission
We have used the Atacama Large Millimeter Array (ALMA) to map the emission of
the CO(6-5) molecular line and the 432 {\mu}m continuum emission from the 300
pc-sized circumnuclear disk (CND) of the nearby Seyfert 2 galaxy NGC 1068 with
a spatial resolution of ~4 pc. These observations spatially resolve the CND
and, for the first time, image the dust emission, the molecular gas
distribution, and the kinematics from a 7-10 pc-diameter disk that represents
the submillimeter counterpart of the putative torus of NGC 1068. We fitted the
nuclear spectral energy distribution of the torus using ALMA and near and
mid-infrared (NIR/MIR) data with CLUMPY models. The mass and radius of the
best-fit solution for the torus are both consistent with the values derived
from the ALMA data alone: Mgas_torus=(1+-0.3)x10^5 Msun and Rtorus=3.5+-0.5 pc.
The dynamics of the molecular gas in the torus show non-circular motions and
enhanced turbulence superposed on the rotating pattern of the disk. The
kinematic major axis of the CO torus is tilted relative to its morphological
major axis. By contrast with the nearly edge-on orientation of the H2O
megamaser disk, we have found evidence suggesting that the molecular torus is
less inclined (i=34deg-66deg) at larger radii. The lopsided morphology and
complex kinematics of the torus could be the signature of the
Papaloizou-Pringle instability, long predicted to likely drive the dynamical
evolution of active galactic nuclei (AGN) tori.Comment: Final version accepted by the Astrophysical Journal Letters
(ApJLetters) on April 27th 2016, 6 pages, 5 figure
Italian Science Case for ALMA Band 2+3
The Premiale Project "Science and Technology in Italy for the upgraded ALMA
Observatory - iALMA" has the goal of strengthening the scientific,
technological and industrial Italian contribution to the Atacama Large
Millimeter/submillimeter Array (ALMA), the largest ground based international
infrastructure for the study of the Universe in the microwave. One of the main
objectives of the Science Working Group (SWG) inside iALMA, the Work Package 1,
is to develop the Italian contribution to the Science Case for the ALMA Band 2
or Band 2+3 receiver. ALMA Band 2 receiver spans from ~67 GHz (bounded by an
opaque line complex of ozone lines) up to 90 GHz which overlaps with the lower
frequency end of ALMA Band 3. Receiver technology has advanced since the
original definition of the ALMA frequency bands. It is now feasible to produce
a single receiver which could cover the whole frequency range from 67 GHz to
116 GHz, encompassing Band 2 and Band 3 in a single receiver cartridge, a so
called Band 2+3 system. In addition, upgrades of the ALMA system are now
foreseen that should double the bandwidth to 16 GHz. The science drivers
discussed below therefore also discuss the advantages of these two enhancements
over the originally foreseen Band 2 system.Comment: 43 pages, 21 figure
Molecular gas in NUclei of GAlaxies (NUGA). XI. A complete gravity torque map of NGC4579: new clues on bar evolution
We create a complete gravity torque map of the disk of the LINER/Seyfert 1.9
galaxy NGC4579. We quantify the efficiency of angular momentum transport and
search for signatures of secular evolution in the fueling process from r~15kpc
down to the inner r~50pc around the Active Galactic Nucleus (AGN). We use both
the 1-0 and 2-1 line maps of CO obtained with the Plateau de Bure
Interferometer (PdBI) as part of the NUclei of Galaxies-(NUGA)-project. We
derive the stellar potential from a NIR (K band) wide field image of the
galaxy. The K-band image, which reveals a stellar bar, together with a high
resolution HI map of NGC4579 obtained with the Very Large Array (VLA), allow us
to extend the gravity torque analysis to the outer disk. The bulk of the gas
response traced by the CO PdBI maps follows the expected gas flow pattern
induced by the bar potential in the presence of two Inner Lindblad Resonances
(ILR). We also detect an oval distortion in the inner r~200pc of the K-band
image. The oval is not aligned with the large-scale bar, a signature of
dynamical decoupling. The morphology of the outer disk suggests that the
neutral gas is currently piling up in a pseudo-ring formed by two winding
spiral arms that are morphologically decoupled from the bar structure. In the
outer disk, the decoupling of the spiral allows the gas to efficiently produce
net gas inflow on intermediate scales. The corotation barrier seems to be
overcome due to secular evolution processes. The gas in the inner disk is
efficiently funneled by gravity torques down to r~300pc. Closer to the AGN, the
two m=2 modes (bar and oval) act in concert to produce net gas inflow down to
r~50pc, providing a clear smoking gun evidence of fueling with associated short
dynamical time-scales.Comment: Submitted for publication in A&A. 21 pages, 21 figure
Learning object relationships which determine the outcome of actions
Peer reviewedPublisher PD
The Science Case for ALMA Band 2 and Band 2+3
We discuss the science drivers for ALMA Band 2 which spans the frequency range from 67 to 90 GHz. The key science in this frequency range are the study of the deuterated molecules in cold, dense, quiescent gas and the study of redshifted emission from galaxies in CO and other species. However, Band 2 has a range of other applications which are also presented. The science enabled by a single receiver system which would combine ALMA Bands 2 and 3 covering the frequency range 67 to 116 GHz, as well as the possible doubling of the IF bandwidth of ALMA to 16 GHz, are also considered
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